1. Field of the Invention
The present invention relates to the hydroxylation of phenols or phenol ethers, and, more especially, to the hydroxylation of phenols or phenol ethers by reacting such starting compounds with hydrogen peroxide in the presence of a germanozeosilite MFI zeolite.
2. Description of the Prior Art
The hydroxylation of phenol or of substituted phenols using hydrogen peroxide, to prepare diphenols, is known to this art.
French Patent No. 69/45,467, published under No. 2,071,464, describes such a process in which the reaction is catalyzed by a strong acid, for example perchloric acid or sulfuric acid.
German Patent No. 2,410,742 describes a process similar to that of the '467 French patent, in which the hydrogen peroxide is employed in the form of an essentially anhydrous organic solution.
The above prior art processes are of considerable interest and the former is carried out industrially.
However, for a number of years attempts have been made to catalyze the hydroxylation reaction using solids which are not dissolved in the reaction mixture, in order to simplify their separation from the reaction mixture to permit their optional recycling and to avoid the saline by-products which are typically formed during the step of removal of the dissolved acidic catalysts.
French Patent Application No. 81/17,023 (published under No. 2,489,816) thus describes the use of titanium silicalite as a heterogeneous catalyst for the hydroxylation of aromatic compounds with hydrogen peroxide.
The fine size of the catalyst particles employed makes their separation from the reaction mixture very difficult and their recycling problematic, whereas, in an industrial process, it is essential that a costly catalyst be recycled.
To overcome this problem of catalyst separation, it has been proposed, in the European Patent Application published under No. 200,260, to employ agglomerates of such finely divided particles of titanium silicalite.
Nonetheless, serious need continues to exist in this art for more effective heterogeneous catalysis of the hydroxylation of phenols or phenol ethers using hydrogen peroxide.